Charging system with low power consumption

1. A charging system comprising: an input voltage supply circuit; a control circuit, coupled to the input voltage supply circuit, and configured to control the input voltage supply circuit to generate an input voltage according to a battery voltage of a target battery; and a charging circuit, coupled to the control circuit, and configured to receive the input voltage and to provide a charging current to charge the target battery, wherein the target battery receives the charging current; wherein the input voltage is generated according to a function that takes the battery voltage as a parameter, and the input voltage is positively correlated with the battery voltage and is greater than the battery voltage; wherein the function is represented as V_in=M×V_BAT+N×R_on×I_cha+K, V_in is the input voltage, V_BAT is the battery voltage, R_on is an equivalent resistance of the charging circuit, and I_cha is the charging current, M and K are positive numbers; wherein a difference between the input voltage and the battery voltage remains constant when the battery voltage is smaller than a threshold voltage, and becomes smaller and smaller when the battery voltage is greater than the threshold voltage.

2. The charging system according to claim 1 , wherein the control circuit and the input voltage supply circuit are arranged in a battery box, the battery box further comprises a power supply battery, and the input voltage supply circuit obtains power stored in the power supply battery to generate the input voltage.

3. The charging system according to claim 2 , wherein the charging circuit and the target battery are arranged in a portable electronic device.

4. The charging system according to claim 3 , wherein the portable electronic device comprises a battery voltage detection circuit which is configured to transmit a value of the battery voltage to the control circuit.

5. The charging system according to claim 1 , wherein the charging circuit is a switch charging circuit.

6. A portable electronic system, comprising: a battery box, comprising: an input voltage supply circuit; a power supply battery, coupled to the input voltage supply circuit; and a control circuit, coupled to the input voltage supply circuit, and configured to control the input voltage supply circuit to obtain power stored in the power supply battery to generate an input voltage according to the battery voltage of a target battery, wherein the target battery receives the charging current; and a portable electronic device, comprising the target battery, and comprising: a charging circuit, coupled to the control circuit, and configured to receive the input voltage and provide a charging current to charge the target battery; wherein the input voltage is generated according to a function which takes the battery voltage as a parameter, and the input voltage is positively correlated with the battery voltage and the input voltage is greater than the battery voltage; wherein the function is represented as V_in=M×V_BAT+N×R_on×I_cha+K, V_in is the input voltage, V_BAT is the battery voltage, R_on is an equivalent resistance of the charging circuit, and I_cha is the charging current, M and K are positive numbers; wherein a difference between the input voltage and the battery voltage remains constant when the battery voltage is smaller than a threshold voltage, and becomes smaller and smaller when the battery voltage is greater than the threshold voltage.

7. The portable electronic system according to claim 6 , wherein the portable electronic device further comprises a battery voltage detection circuit which is configured to transmits a value of the battery voltage to the control circuit.

8. The portable electronic system according to claim 6 , wherein the charging circuit is a switch charging circuit.